Prolonged excitation of individual neocortical neurons, structure of background impulse activity

The background impulse activity of individual neurons was recorded extracellularly in the cerebral cortex of the cat during the prolonged microionophoretic delivery to these neurons of L-glutamate. Glutamate ionophoresis ensured the transition of the neuron to an elevated, but stable level of activation. An autocorrelation analysis of the trains of impulses showed that in spite of the multiple rise in the average discharge frequency, the type of background impulse activity and the periods of increased and reduced probability of discharges for the most part remained constant. The obtained data indicate that an individual cell is unable to influence substantially the interneurons connected with it, while the type of background activity of a neuron is determined primarily by the level of activation of the cellular ensemble incorporating this neuron.